The present invention generally relates to turbomachinery rotors, and more particularly to an apparatus configured to enable multiple service operations to be performed on a turbine rotor while the rotor remains continuously supported with the apparatus.
Depending on design considerations and their operating conditions, turbomachinery rotors used in steam turbines, gas turbines, and jet engines may have assembled or monolithic constructions. For example, large steam turbines typically have a bolted construction made up of separate rotors, each having a shaft with an integrally-formed wheel. Rotors for gas turbines and jet engines are often constructed by bolting a series of disks and shafts together. Another rotor construction involves welding together rotor segments formed of dissimilar materials, forming what may be termed a multiple alloy rotor (MAR). Monolithic multiple alloy rotors have also been proposed. In each case, the rim of the wheel (disk) is configured for mounting buckets (blades). A conventional mounting technique is to form slots having dovetail cross-sections configured to interlock with complementary dovetail features on the root portions of the buckets.
Turbine rotors operate at high rotational speeds in a thermally-hostile environment. Though significant advancements have been made in alloys to achieve long service lives, wear, erosion, corrosion, shock, fatigue and/or overstress inevitably occur, necessitating periodic inspection and, if necessary, repair or replacement of a rotor or its components. The dovetail region of a wheel is particularly susceptible to cracking as a result of the rim being subjected to higher stresses. Inspection and servicing of large steam turbine rotors and their components typically entail removing the rotor from the steam turbine and transporting the rotor to a service center, incurring cost and cycle time. At the service center, the rotor is mounted on a lathe or a similar lathe-type apparatus adapted to rotate the rotor about its axis. The rotor is typically supported along its length with pedestals that help support the weight of the rotor without interfering with its ability to rotate. The rotor then undergoes the desired service operation, which may include cleaning, dimensional inspection, nondestructive examination (NDE), disassembly/assembly, machining, welding, stress relief, or balancing. These operations typically involve incrementally rotating the rotor to remove the buckets, incrementally or slowly rotating the rotor to remove damaged dovetail regions, perform a welding operation to build up material on the machined surfaces, stress relieve the weld buildup, and machine the weld buildup to reform the dovetail regions, and finally rotating the rotor at a speed sufficiently high to determine rotor alignment, from which balance weights can be added to the rotor to ensure that the rotor is balanced for rotation about its axis.
Because of the different capabilities required for a given service operation, separate workstations are typically used to perform the various operations, for example, a lathe, mill, weld positioner, low-speed balance pit, etc., to perform the necessary operations. Each transfer between workstations requires breaking the previous setup, performing a new setup, and transporting the rotor between workstations by crane, train, tractor trailer, crawler, etc. It is not uncommon for a rotor to sit in a queue waiting for a nondedicated tool or workstation to be available to perform the next operation on the rotor.
From the above, it can be appreciated that the use of dedicated rotor workstations incurs considerable cycle time and cost. Drawbacks of the conventional service approach have been addressed in part by establishing workstations dedicated to multiple operations, such as machining and welding, to reduce setup times, establish a more continuous flow through the process, and eliminate some queues in the system. However, such workstations have not been adapted to perform operations at which widely different rotational speeds are required, for example, when performing a dynamic balancing operation. Such workstations have also not typically lent themselves to installations outside of a service shop, and the service process still requires movement of a rotor through multiple process steps.